The sense of taste, e.g., in human, can detect at least five traditional tastes: sweet, sour, salty, bitter, and umami (savory). Many nutritious substances including vegetables, foods, food ingredients and nutrients comprise bitter tastants and/or have a bitter taste. In addition, many pharmaceutical substances important to maintain or improve health comprise bitter tastants and/or have a bitter taste. While certain food products and consumer products have desirable bitter tastes, including coffee, beer and dark chocolate, in many contexts, consumers dislike such bitter tastes. For example, many consumers dislike the perception of certain bitter tastants and/or bitter taste and will avoid food or pharmaceutical products with an undesirable bitter tastant or bitter taste in favor of food and pharmaceutical products that have reduced levels of undesirable bitter tastants or that have reduced or that completely lack bitter taste. This aversion to products containing undesirable bitter tastants and/or having undesirable bitter taste may be caused by perception of bitter tastants and/or bitter taste mediated by activation of bitter taste receptors present in the oral cavity and/or in the gastrointestinal tract. In many cases, consumer dislike of bitter tastants and/or bitter taste prevents or hampers improvement of the nutritive quality and safety of foods as desired levels of nutrients or preservatives comprising bitter tastants and/or having bitter taste cannot be used. Also, dislike of or aversion to the bitter tastants or bitter taste of some pharmaceutical agents negatively impacts compliance with prescribed regimens for their use.
For instance, several additives, preservatives, emulsifiers and foodstuffs used in the production of food products comprise bitter tastants and/or have a bitter taste. While these additives, preservatives, emulsifiers and foodstuffs may affect the taste of a food product, they may also be important for improving the shelf life, nutritive quality, or texture of the food product. For example, the increasing trend of hypertension and cardiovascular disease has been attributed, in part, to the high sodium intake of the Western diet. Accordingly, substitution of sodium chloride with another salty tasting compound is desirable. The most common sodium chloride substitute is potassium chloride, which, to a portion of the population, is perceived as possessing a bitter taste in addition to its salty taste. The bitter taste of potassium chloride limits the extent to which it may be used to replace sodium chloride in foods without causing undesired bitter taste for the portion of the population sensitive to it.
Another common food additive, sodium lactate, has a broad antimicrobial action, is effective at inhibiting spoilage, and growth of pathogenic bacteria, and is commonly used in food products (e.g., meat and poultry products) to extend shelf life and increase food safety. Due to its sodium content, however, sodium lactate, can be undesirable as a preservative. Potassium lactate, which has similar antimicrobial properties, has been used in lieu of sodium lactate. However, potassium lactate is also associated with a bitter taste which limits the extent to which it may be used to replace sodium lactate in foods without causing undesired bitter taste.
In addition, the increasing incidence of obesity and diabetes has been attributed, in part, to the high sugar intake of many diets. Accordingly, substitution of sugar with another sweet tasting compound is desirable. Artificial and natural sugar substitutes that may be used to reduce sugar in foods are often associated with bitter taste which again limit the extent to which these may be used to replace sugar in foods without causing adverse bitter taste. For example, a common sugar substitute is Acesulfame K, which also has a bitter taste in addition to its sweet taste.
Without being limited by theory, bitter, sweet, and umami tastants and compounds typically elicit a taste response via G-protein coupled receptors, while salty and sour tastants and compounds are typically hypothesized to elicit a taste response via ion channels. Bitter taste receptors belong to the TAS2R (also referred to as T2R) family of G-protein coupled receptors that induce intracellular calcium concentration changes in response to a bitter tastant. TAS2R receptors act via gustducin, a taste-specific G-protein. There are at least twenty-five different members of the TAS2R family, suggesting that the perception of bitter taste is complex, involving several different tastant-receptor interactions. Some of the TAS2R members, e.g., TAS2R60, are orphan receptors, which have not had a ligand identified. Compounds capable of modulating the activation and/or signaling of bitter taste receptors in the oral cavity and/or the gastrointestinal tract could be effective to allow desired usage levels of bitter tastants or bitter tasting substances in food and pharmaceutical products without resulting in consumer dislike of such products due to perception of the increased levels of bitter tastants or bitter tastes. In some instances, blockers or modulators of bitter taste receptors and bitter taste may reduce the perception of bitter tastants and/or bitter taste via the bitter taste receptors and/or taste transduction signaling machinery present in the oral cavity and/or the gastrointestinal tract.
Traditionally in food preparation and pharmaceuticals, bitter taste was masked using sweeteners and other tastants, including salt. In some cases, however, this is undesirable or insufficient because it can alter, mask, or interfere with other tastes/flavors/impressions (e.g., non bitter tastes or desired bitter tastes) in the food product. Additionally, this approach has rarely been able to completely mask the bitter taste present in such food products or pharmaceuticals. For that reason, compounds which reduce bitter taste instead of, or in addition to, masking agents are preferred.
It is, therefore, desirable to provide assays to identify compounds that may be added to food products, consumer products and pharmaceuticals comprising bitter tastants or having a bitter taste to eliminate, modulate or reduce the perception of the bitter tastants or bitter taste or to reduce the corresponding activation of the bitter taste receptors in the oral cavity and/or the gastrointestinal tract. Similarly, it is desirable to identify compounds that do not activate other bitter taste receptors (i.e., compounds having off-target affects).